Insular Evolution
As islands are usually separated from a larger landmass or continent, life on larger islands tend to diversify without little interference from it's main landmass or other continents. Insular environments are known to have unique and "odd" life compared to the mainland, making them famous in evolution. Island Colonization Largely the first animals to reach islands are flying animals, such as birds and bats, if a mammal is not already established on the island, mammals such as dolphins or pinnipeds are likely to be the largest mammals in that island region. Animals evolve differently on an island depending on habitat, size and species. For non-flying or swimming animals, rafting or drifting across oceans, being swept by currents, is generally the method in which they happen upon archipelagos and islands. This has the implication of a given species that arrives on the island having only a handful of individuals. Lemurs, for example, are thought to have descended from a little over a dozen individuals. The implication that rafting is the best way to get to an island means many insular habitats have few or no terrestrials mammals aside from bats; repties, particularly tortoises, have been noted to be far better at getting to islands then mammals of the same size in a given habitat; and flightless birds have been known to also get to close offshore islands, thought are also not good at crossing large distances over water, perhaps indicating metabolism plays a part in rafting success. Indeed, at least some mammals that have gotten to islands have been noted to be capable of hibernation, at least when they would've arrived on the island| Mouse Lemur Factsheet Insular Evolution Insular dwarfism is an evolutionary process that conditions the reduction in size of large animals over a number of generations when their population's range in a limited amount of land, usually islands. Sometimes if a predator does not exist on a mainland, a smaller animal will become larger and take over the niche as a predator. Island gigantism is an evolutionary process which usually involves a smaller animal increasing in size over an amount of generations to fill an ecological role otherwise occupied by another species. Adaptive Radiations In addition, adaptive radiations are a common result of an organism entering an entirely new set of niches on an island which has these spots vacant. Adaptive radiation is where a single species diverges to take up different ecological roles or to simply survive in an island. Take Darwin's finches, multiple species of finch in the Galapagos that all diverged from an common ancestor based on what area of the island they inhabited. Sometimes islands are the only way for living fossils to become as diverse as they may have been before a dominant family or group took over the niches, as seen with lemurs. Originally lemurs diverged form a single species that started to split off and fill different roles in different habitats; ancestral African lemurs went extinction several tens of millions of years ago. Similarly, but on a much larger scale, marsupials diversified in Australia, taking up many different types of niches, such as herbivores, insectivores and carnivores; whilst the placentals took control elsewhere. Introduction & Feral Species Islands that have species introduced by humans can cause there existing ecosystems to become unstable. Though it may be evolutionarily possible for an animal to be established in the ecosystem or evolve to suit that ecosystem. In New Zealand, a large amount of mammals have been established that are pushing many bird species out of their ecological roles. It is safe to assume in the future, mammals will start to take up more ecological roles on the archipelago than they did pre-human colonization. Goats are among the most common of these feral species. Cats, pigs, dogs, rats, chickens, ferrets, weasels, and several other species closely allied to man are also common examples. In many cases, the insular fauna isn't used to predators (cats, mongoose, weasels, ferrets, dogs, etc), are succeptiple to brought illnesses (rats), or the ecosystem has never experienced large or even mid-sized herbivorous mammals; often no mammals at all. Extinction The arrival of man and feral animals has caused the majority of island species across the globe to become endangered or even extinct, and commonly entire ecosystems have been destroyed by these "assaults" by man. There are several ways in which this can happen, commonly man will eat the local creatures, and their animals will have a much larger effect on the ecosystem. It is commonly noted across several historical accounts, covering several different islands and species, that these creatures on predator-less environments are not at all scared of man, and indeed are completely docile and calm natured, having no fear of humans ReferencesCategory:Tutorial